mdiff.patch(): add a special case for when the base text is empty

remove the special casing from revlog.addgroup()

mercurial/mdiff.py

@@ -260,6 +260,9 b' def patchtext(bin):'
     return "".join(t)
 
 def patch(a, bin):
+    if len(a) == 0:
+        # skip over trivial delta header
+        return buffer(bin, 12)
     return mpatch.patches(a, [bin])
 
 # similar to difflib.SequenceMatcher.get_matching_blocks

mercurial/revlog.py

@@ -1353,12 +1353,7 b' class revlog(object):'
                         dfh.flush()
                     ifh.flush()
                     text = self.revision(chain)
-                    if len(text) == 0:
-                        # skip over trivial delta header
-                        # text == '' in the case of nullrev or punched revision
-                        text = buffer(delta, 12)
-                    else:
-                        text = mdiff.patches(text, [delta])
+                    text = mdiff.patch(text, delta)
                     del delta
                     chk = self._addrevision(node, text, transaction, link,
                                             p1, p2, None, ifh, dfh)